The invention relates to a self-attaching fastener and more particularly to a threaded fastener that is forcibly mechanically interlocked or clinchingly attached to a portion of sheet material, and to apparatus and a method of assembly thereof.
Reference is made to my related patent application, Ser. No. 184,951, filed Sept. 8, 1980, now abandoned the disclosure of which is incorporated by reference herein. The present invention disclosed herein includes variations on the inventive principles disclosed in said related application.
It is frequently desirable to secure objects to a member formed from a relatively thin sheet of material, such as sheet metal. Because such sheet material is generally too thin to form a threaded hole therein by drilling and tapping, a threaded female fastener or nut is frequently welded or otherwise secured to such sheet material, thus allowing a male fastener to be threadedly secured thereto.
Alternatively, it may be desirable to provide a threaded male fastener extending from such sheet material in order to allow another object to be mounted thereto by means of a threaded female fastener. In such a case, the head of a bolt may be welded or otherwise secured to such sheet material.
In one known method of securing a threaded fastener to sheet material, a specially formed clinch nut is fabricated with a pilot portion extending from one of its faces. The pilot is smaller than the remainder of the nut and thus forms one or more shoulder portions thereon. The pilot is inserted into a preformed opening in the sheet material and deformed to flow outwardly, thereby interlockingly engaging the edges of the performed hole in the sheet material.
In another method of securing a threaded fastener to sheet material, a specially formed pierce nut with a pilot is provided which is specially adapted to pierce or punch an opening as the nut is forcibly urged against the sheet material. Specially formed dies on a press apparatus deform the sides of the pilot and the opening in the sheet material to form a clinch-type engagement therebetween. Such specially formed and fabricated pierce nuts may also include shoulders on the main portion of the nut for abuttingly engaging the sheet material in order to attain a more even stress distribution, thereby stengthening the joint between the nut and the sheet material.
The above-described methods and apparatus for securing a fastener to sheet material suffer the disadvantage of requiring an expensive specially formed nut or fastener. Such methods and apparatus also tend to weaken the sheet material because of the necessity of removing a substantial amount of sheet material in order to form the opening in which the fastener is received. In a high production environment, they also create a considerable amount of scrap.
The present invention overcomes the above disadvantages by allowing standard fasteners such as ordinary nuts or bolts to be secured to a sheet material member, thereby eliminating the need for the expensive special fasteners described above. In the disclosed embodiment of the invention, a standard off-the-shelf square nut or a square-headed bolt is secured to such sheet material, frequently without preforming an opening in the sheet material, thereby eliminating or minimizing the attendant scrap. In accordance with the present invention, the sheet material is sheared by means of the coactive force of a pair of cutting members and the edges of the fastener along opposite sides of the fastener to form a support strap therebetween. This strap, which remains integral with the sheet material, is simultaneously forcibly urged into an offset position relative to the plane of the remainder of the sheet material and preferably abuttingly conforms to at least one of the faces of the fastener. The opposite sides of the fastener, adjacent the sheared portion of the sheet material, are deformed to interlock the fastener to the sheet material.
Thus the present invention provides a method and apparatus by which ordinary fasteners can be rigidly secured or attached to a sheet material member without the need for specially formed fasteners. Furthermore, because the only sheet material removed (if any) is that resulting from the punching of a hole in the support strap which corresponds to the aperture through a female fastener, or which receives the stud portion of the male fasteners, the sheet material is not substantially weakened by the forming or pressing operation and significantly less scrap is generated.
These and other advantages of the invention will become readily apparent from the following discussion and the accompanying drawings.